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More Inheritance

Stay updated with important dates for Inheritance, attend the Project 1 review session, and learn about pair programming benefits and techniques.

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More Inheritance

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  1. More Inheritance 7/2/2009

  2. Important Dates • Project 1 - Check-off • Thursday 7/02/2009 ready BEFORE lab • Review Session • Sunday 7/05/2009 – 306 Soda 1-4pm • Midterm 1 • Tuesday 7/07/2009 – 10 Evans 5-6pm • Covers everything through Monday’s lab • Project 2 released • Thursday 7/09/2009 • Project 1 due • Monday 7/13/2009 – 10pm

  3. equals(Object o) Did you understand Wednesday’s lab?

  4. ← Uses a1’s dynamic type Animal a1 = new Dog(); Animal a2 = new Dog(); Dog d1 = new Dog(); a1.sniff(d1); d1.sniff(a1); a1.sniff(a2); ← Uses a1’s static type ← Uses a1’s dynamic type Uses a2’s static type

  5. Inheritance • Compilation: • CALLER: It makes sure that the static type of the object has the appropriate method • ARGS: It makes sure that the method takes in the static type of the arguments • Run-time: • CALLER: When you call a method on an object it looks for the method starting at the object’s dynamic type • ARGS: When you pass an object as an argument, it looks for a method with that static type

  6. Dog age bites Animal a1 = new Dog(); Animal a2 = new Dog(); Dog d1 = new Dog(); a1.sniff(d1); d1.sniff(a1); a1.sniff(a2); 0 true Dog age bites 0 main Animal a1 Animal a2 Dog d1 true Dog age bites 0 true

  7. What about equals(Object o) ArrayList was using an Object reference Object o1 = new Animal(); Object o2 = new Animal(); o1.equals(o2); If others will call your methods with more generic references, you want to provide a method that takes in an Object

  8. Regular Inheritance (extends)

  9. Animals Pets Eat Bananas

  10. Interfaces • I have a GREAT idea! • Everyone will want to make Pets that can • eatKibble() • sitOnLap() • How?!?! • I don’t care!!!!

  11. Animals Pets Eat Bananas

  12. The Petinterface

  13. Dog can implementthe Petinterface

  14. Cat can implementthe Petinterface

  15. We can have a Petremote control(Pet reference) Pet p1 = new Dog(); Pet p2 = new Cat(); p1.eatKibble(); p2.sitOnLap();

  16. Can we have a Pet object? Pet p1 = new Pet(); No! You can’t create an object of an interface!

  17. Interfaces can be cool!!!

  18. Example • The sort method of the Array class promises to sort an array of objects, but under one condition: the objects in the array must implement the Comparable interface: public interface Comparable { intcompareTo(Object other); }

  19. Summary of Interfaces • Interfaces don’t implement ANY methods • Just put a semicolon at the end of the method • Classes can implement multiple interfaces • To implement an interface you must write all of the methods that the interface defines

  20. Cookies!

  21. Abstract Classes (less lazy than Interfaces) • I have a GREAT idea! • Everyone will want to make Cookies that can have these methods: • ingredients() • isDelicious() • How?!?! • isDelicious() is pretty simple, I’ll write that one • ingredients() ?!? Sounds too hard! I’ll make that abstract

  22. Abstract Class Cookie

  23. ChocolateChipCookie can extend the Abstract class Cookie

  24. GirlScoutCookiecan extend the Abstract class Cookie

  25. We can have a Cookie remote control(Cookie reference)

  26. Can we have a Cookie object? Cookie p1 = new Cookie(); No! You can’t create an object of an abstract class!

  27. Abstract Class Summary • Label an Abstract class as abstract • Label any methods that you don’t want to implement as abstract • Your children MUST write all of the abstract methods • Instance variables in the abstract class will be available in the child class • You can only extend one Class (abstract or otherwise)

  28. How to do Pair Programming? • Share one computer with your partner. • The “Driver” types and uses the mouse. • The “Navigator” watches, discusses and focuses on the big picture. • Take turns (about every 30 minutes) to switch roles.

  29. Why to do Pair Programming? • Writing code is easy compared to making code work! • The bugs are the part that takes a long time • Clearer programs, better designs, fewer bugs. • Great to talk about at an interview! • “Overcoming difficult problems” • Research Study – Error free code went from 70% to 85% with pairs. So 30% to 15% or a 50% reduction in bugs. Source: Wikipedia: Pair Programming

  30. Working with Partners • Use pair programming! • Talk about other commitments • Travel plans • Other classes • Jobs • Assume that if you haven’t seen their code – it doesn’t exist! • Talk to your partner the moment you get stuck

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